1. Field of the Invention
In one aspect this invention relates to supplemental heaters for use in vehicles. In a further aspect, this invention relates to multifuel heaters using a external combustion air supply and external exhaust for use in vehicles.
2. Prior Art
The use of supplementary, forced air heaters in vehicles is well known. In military vehicles such heaters are subject to extreme environmental conditions of heat and dust not encountered by normal vehicles.
One example of a useful forced air heater is disclosed in U.S. Pat. No. 3,523,004. This patent discloses a heater configuration with a casing forming a combustion chamber and having an associated blower for forcing combustion air longitudinally through the combustion chamber. The burner has an apertured plate located transversely across the casing to direct the combustion air along predefined longitudinal paths. A cupped shaped member is positioned down stream from the plate with its open end directed toward the apertured plate to receive incoming combustion air. A ceramic wick is coaxially mounted in the combustion chamber inside the cup with a small space between the cup and the porous wick. The ceramic wick has a fuel source which feeds liquid fuel to the wick for vaporization and combustion.
Burners of this configuration have demonstrated good performance characteristics under various conditions; however, they can have problems with the dust and debris commonly found in battlefield environments, especially desert environments. This is particularly true since the combustion air supplied to the blower is drawn from the ambient atmosphere and is generally unfiltered. Filtration of the air to remove particulate material is normally not practicable as it would cause a large pressure drop in the air intake. The particles in the combustion air will clog the apertured plate and other air passages in the burner until the quantity of combustion air is reduced and the heater will be partially destroyed. The debris problem is particularly acute when the burner has an ignition wick which transports a quantity of fuel from the porous ceramic wick to an ignition cup. Because of the tolerances involved, the presence of dirt in combustion air furnished to the ignition cup can hamper heater start-up and continuing function.